Typically, a seat for vehicles includes a slide mechanism that can move forwards and backwards to conform to the body shape of an occupant of the vehicle and a recliner that can adjust a tilt angle of a seat back. The slide mechanism typically refers to a device that enables forward and backward adjustment of the position of the vehicle seat. Such a typical seat slide mechanism basically includes a lower rail that is securely fixed to a vehicle body. An upper rail is rested on the lower rail and is movable forwards and backwards together with a seat cushion frame. A locking assembly serves to selectively perform a locking and an unlocking between the lower rail and the upper rail and an operating lever enables locking and unlocking of the locking assembly.
Several seat slide mechanism have been designed to improve upon this basic configuration, such as for example, Korean Patent Registration No. 374650 (Feb. 20, 2003). This registration discloses an improved locking assembly which attains structural simplicity, lightness in weight, improved fastenability, etc. The locking assembly is constructed such that a J-shaped hook attached to the upper rail and a ┐-shaped lower rail are fastened to each other along with a locker guide.
Also, Korean Patent Laid-Open Publication No. 2004-45538 discloses an improved locking assembly which includes a lever means, a locker operated cooperatively with the lever means, and an anti-shift bar so as to attain improved convenience in operation and high-grade functionality. The locking assembly is constructed such that a plate-shaped locker engages a locking hole formed at the lower rail so as to perform the operational confinement between the upper rail and the lower rail.
In addition, Korean Patent Laid-Open Publication No. 2004-26476 discloses an improved seat track structure for vehicles that includes a locking assembly. A locking plate is integrally coupled with a slide lever hingeably fixed to a side of the upper rail and moved vertically to lock and unlock into and from a hole formed at the lower rail so as to prevent its structural deformation and increase stability.
Such locking assemblies of the seat slide mechanism employs either a horizontal locking scheme that enables a locking and an unlocking between the upper rail and the lower rail depending on rightward and leftward movement of a locker or a vertical locking scheme which enables a locking and an unlocking between the upper rail and the lower rail based on upward and downward movement of the locker. The shape of the locker may be modified into various shapes including a plate-type hook shape, a plate-type trapezoidal shape, etc.
In the meantime, in the case where an RV or SUV vehicle has a seat arrangement of three rows or more, a two-person bench seat (6 side seat in a division ratio of 6 to 4) is applied to the second and third row seat. European countries stipulate an application of a three-point type seat belt for the middle seat to the second and third row seat. However, the conventional seat slide mechanism, intended to provide convenience to a passenger occupant seated on the second and third row, is structured such that it does not endure a mechanical strength of 3.2 ton/1 person required at the time of applying a three-point type seat belt for the middle seat.
That is, for such a conventional seat slide mechanism, there occurs a problem in that since it is structured to be applied to a one-person seat, if it is applied to a two-person bench seat, the seat slide structure is easily damaged (i.e., separated or widened) due to insufficient mechanical strength. Particularly, in the case where the three-point type seat belt for the middle seat is applied to the two-person bench seat, the slide mechanism is apt to be easily damaged as a result of its insufficient mechanical rigidity.
Furthermore, the conventional locker is formed of a plate-type hook shape or a plate-type trapezoidal shape. This does not sufficiently meet the mechanical strength required at the time of applying a three-point type seat belt for the middle seat. Moreover, in the case where an existing plate-type hook shaped (particularly, a horizontal locking scheme) locker is applied, there intermittently occurs a half-locked condition. As a result, when the body weight of a passenger is exerted to the seat or the seat is slightly moved due to inertia during traveling, the upper rail and the lower rail are often locked to each other while producing a “snap” sound. This contributes to serious deterioration of stability. There is therefore a need for an improved solution against the above drawbacks.